reset: microchip-sparx5: issue a reset on startup

Originally this was used in by the switch core driver to issue a reset.
But it turns out, this isn't just a switch core reset but instead it
will reset almost the complete SoC.

Instead of adding almost all devices of the SoC a shared reset line,
issue the reset once early on startup. Keep the reset controller for
backwards compatibility, but make the actual reset a noop.

Suggested-by: Philipp Zabel <[e-mail]>
Signed-off-by: Michael Walle <[e-mail]>
Tested-by: Steen Hegelund <[e-mail]> on Sparx5
Signed-off-by: Philipp Zabel <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]

drivers/reset/reset-microchip-sparx5.c

···
 	.reg_stride	= 4,
 };
 
-static int sparx5_switch_reset(struct reset_controller_dev *rcdev,
-			       unsigned long id)
+static int sparx5_switch_reset(struct mchp_reset_context *ctx)
 {
-	struct mchp_reset_context *ctx =
-		container_of(rcdev, struct mchp_reset_context, rcdev);
 	u32 val;
 
 	/* Make sure the core is PROTECTED from reset */
···
 					1, 100);
 }
 
+static int sparx5_reset_noop(struct reset_controller_dev *rcdev,
+			     unsigned long id)
+{
+	return 0;
+}
+
 static const struct reset_control_ops sparx5_reset_ops = {
-	.reset = sparx5_switch_reset,
+	.reset = sparx5_reset_noop,
 };
 
 static int mchp_sparx5_map_syscon(struct platform_device *pdev, char *name,
···
 	ctx->rcdev.of_node = dn;
 	ctx->props = device_get_match_data(&pdev->dev);
 
+	/* Issue the reset very early, our actual reset callback is a noop. */
+	err = sparx5_switch_reset(ctx);
+	if (err)
+		return err;
+
 	return devm_reset_controller_register(&pdev->dev, &ctx->rcdev);
 }
 
···
 	return platform_driver_register(&mchp_sparx5_reset_driver);
 }
 
+/*
+ * Because this is a global reset, keep this postcore_initcall() to issue the
+ * reset as early as possible during the kernel startup.
+ */
 postcore_initcall(mchp_sparx5_reset_init);
 
 MODULE_DESCRIPTION("Microchip Sparx5 switch reset driver");